Nope, entirely unrelated, she's the princess of a kingdom he defeated but she wasn't a "recognised" princess so not many know what she looks like but she's known for good deeds etc.
Nope they aren't. He conquered her royal family. Meaning he killed her family and took over their kingdom. So he's from a different empire, kingdom or whatever it is.
They're not siblings right??
I'm too lazy to re-read everything to confirm, so I'mma just ask here
By they I mean MC and crown prince